1. Field of the Invention
The present invention relates to a method for purifying L-glutamine (L-Gln) which is used as a starting material for medicinal agents and for other purposes.
2. Description of the Background
L-glutamine can be prepared by organic synthesis, but its synthesis by fermentation has advanced in recent years, producing the compound in high efficiency. L-glutamine tends to undergo decomposition under certain temperature and pH conditions to form pyrrolidonecarboxylic acid (PCA), and once PCA is formed, it is practically impossible to restore L-glutamine from this decomposition product. Hence, scrupulous care must be taken in purifying this compound.
The so-called "resin-treatment process" has been generally used for isolating L-glutamine from its fermentation liquor, in which the liquor is directly, or after removal of microbial cells by a separator of centrifugal or filtration type, brought into contact with a strongly acidic cation-exchange resin to adsorb L-glutamine, followed by elution with an alkaline solution and crystallization. This is an excellent process for isolating and purifying L-glutamine because most of the impurities contained in its fermentation liquor, such as foreign amino acids, PCA (a decomposition product of L-glutamine), microbial cells, soluble proteins, inorganic salts and sugars left unconsumed, can be removed unadsorbed.
The conventional process, however, has problems, which are industrially quite significant, which are that much water is necessary for reactivation and washing of the ion-exchange resin, imposing a big burden for waste water treatment, and that chemical decomposition of L-glutamine is likely to occur as a result of its contact with acids and alkalis in resin treatment resulting in a low recovery rate from the fermentation liquor. A need therefore continues to exist for an improved method of purifying L-glutamine.